1. Technical Field
This invention relates to a charging member, and a process cartridge and an electrophotographic apparatus which make use of the same.
2. Background Art
In electrophotographic apparatus, in order to stably charge a drum-shaped electrophotographic photosensitive member (hereinafter simply “photosensitive member”) electrostatically, it is common to apply to a charging member disposed in contact with the electrophotographic photosensitive member an alternating-current voltage in the state it is superimposed on a direct-current voltage. As one of problems in such a charging system, vibration noise is given which is caused by the resonance that exists between the photosensitive member and the charging member.
To cope with such a problem, a method is proposed in which a charging member having a natural vibration frequency at which no resonance may arise due to the frequency of the alternating-current voltage to be applied is used so as to prevent the vibration noise from being caused, as disclosed in Japanese Patent Application Laid-open No. 2004-279578. Now, in recent years, with demand for electrophotographic apparatus to be made higher in image quality and higher in process speed, it has come to be that an alternating-current voltage with a high frequency of, e.g., about 3,000 Hz is applied to the charging member.
The photosensitive member is also rotated at a high speed, with which rotation a motor itself that drives the photosensitive member vibrates and also gears and so forth that transmit the driving force of that motor vibrates. Such vibrations not only cause charging noise, but also vibrate the charging member disposed in contact with the photosensitive member, to make it difficult for the photosensitive member to be stably charged to a stated potential, and, as the result, lower the grade of electrophotographic images in some cases. Under such circumstances, the present inventors have come to the realization that development must be made on techniques which are to more surely reduce the vibration of the charging member.